1. Field of the Invention
This invention relates generally to a locking device, and particularly to locking devices which are adapted to cover the prongs of an electrical outlet to prevent the unauthorized use of an electrical apparatus or appliance associated with the electrical plug.
2. Description of the Prior Art
Electrical plug locking devices are generally known and have been invented to limit or control the use of certain apparatus and appliances, either because of danger associated with the use of certain apparatus or to limit the time of operations of appliances and apparatus.
A locking device for an electrical plug is shown in U.S. Pat. No. 2,664,734, wherein a locking housing contains an internal locking mechanism which is adapted to trap and lock the prongs of an electric plug inserted into the housing. Although this known device performs satisfactorily if undue force is applied to the electric plug, it can be wrenched out of the housing under certain occasions, and sometimes the internal locking mechanism can be forced out.
Another disadvantage of the known device is that the internal locking mechanism is made of metal parts which may present a hazardous condition to someone tampering with the locking device.
Another form of a known locking device for electric plugs is described in U.S. Pat. No. 2,654,073. This known device has a housing provided with a pair of slots for the insertion of the prongs of a plug, and has an internally-contained locking mechanism which is capable of locking only one of the prongs. Since one of the prongs is relatively loose, this encourages tampering by children, which may result in damage to the plug and the locking mechanism. The locking mechanism is complex because it uses a regular key and a barrel with a plurality of pins, and this would involve unusual expense in manufacturing.